Google Apps Script: Upload a File to Google Drive via HTTP POST

index.gs

// https://developers.google.com/apps-script/guides/web
//
function doPost(e) {
  if (!e.parameter.filename) {
    return HtmlService.createHtmlOutput("Don't forget a filename parameter in the URL!");
  }
  if (!e.postData.contents) {
    return HtmlService.createHtmlOutput("No POST data received :(");
  }
  // create a new folder in Google Drive
  // DriveApp.createFile(name, content, mimeType)
  var drivefile = DriveApp.createFile(e.parameter.filename, e.postData.contents, e.postData.type);
  
  // drive files aren't actually "in" folders. they're treated like gmail messages and labels.
  // in gmail, one message can have multiple labels.
  // in drive, one file can have multiple folders.
  // more explanation here: https://www.labnol.org/internet/add-files-multiple-drive-folders/28715/
  // here, i remove the file from the root folder and add it to a custom folder specified.
  DriveApp.getRootFolder().removeFile(drivefile);
  var folder = DriveApp.getFolderById('1vZOE5wXXEq5DV4ljfY7-7vctASDf786asdf').addFile(drivefile);
  
  return HtmlService.createHtmlOutput("File added successfully to the " + folder.getName() + " folder!");
}